This invention relates to imaging devices, particularly but not exclusively so-called hybrid devices which may comprise infrared detector elements of, for example, cadmium mercury telluride coupled to charge-integration means in, for example, a silicon circuit body. Such devices may be used in so-called "solid-state" video cameras and may operate at infrared wavelengths, for example in the 3 to 5 .mu.m (micrometers) or 8 to 14 .mu.m bands.
In European patent application (EP-A) No. 0 128 828, there is disclosed an imaging device comprising (a) a plurality of photodetector elements which generate charge carriers in response to incident photon radiation, (b) charge-integration means coupled to each photodetector element for temporarily storing and so integrating charge generated at that detector element during an integration period, (c) signal-deriving means for deriving a signal from said charge-integration means in accordance with the amount of charge integrated at the charge-integration means, and (d) reset means for resetting the charge-integration means before the beginning of each integration period.
In the devices disclosed in EP-A No. 0 128 828, the current from each detector element is integrated on an associated capacitor and an output signal is derived by measuring the capacitor potential using individual voltage-reading means (for example source-follower MOS transistors M11, M21, M31, M41 in FIG. 1 of EP-A No. 0 128 828) which are individually sequentially switched (for example by addressing MOS transistors M12, M22, M32, M42 in FIG. 1 of EP-A No. 0 128 828). Individual reset means (for example MOS transistors M13, M23, M33, M43 in FIG. 1) are associated with each capacitor and in particular EP-A No. 0 128 828 discloses an interconnection of the individual switching means (for example M22) with the individual reset means (for example M13) of the preceding capacitor so that as the voltage from one capacitor is read the preceding capacitor is reset. This provides a simple automatic arrangement for resetting the preceding capacitor, but it has been noted by one of the present inventors that when there is a variation in the supplied reset voltage (due to noise or interference, for example) a corresponding variation of the output signal can result when the reset capacitor is subsequently read. Since the integration time for the imaging devices in EP-A No. 0 128 828 excludes the reset time, the signals from different detector elements are integrated at different times so that the detector elements do not stare coincidentally.